FIG. 1 illustrates the equipment usually used in monitoring the blood pressure of a patient at some point in his blood circulation system. One end of a catheter C is inserted through the blood vessels to that point, and the other end is connected to a port on a t connector 2. A bottle 3 of saline solution is coupled via a tube 4, a valve V1 and a fast/slow flush device f to another port of the t connector 2, and a third port of the t connector 2 is coupled via a tube 5 and a valve V.sub.2 to a hollow cavity c in what is called a pressure dome D. A tube 6 that communicates with the cavity c is provided with a valve V.sub.3, and the cavity c is covered by a pliable membrane m. A transducer T is provided that converts any pressure applied to its sensing surface S that is in contact with the membrane m into a corresponding electrical signal. An exciting voltage that is required by the type of transducer used is supplied by a monitor M via leads L.sub.1 and L.sub.2, and the output pressure signal from the transducer T is coupled to the monitor M by leads L.sub.3 and L.sub.4 so as to control a pressure indicator I. The monitor M and the transducer T may be at some distance from each other.
After the catheter C, the tubes 5 and 6 and the cavity c have been filled with saline solution, a zero setting of the monitor pressure indicator is attained by the following steps. This procedure will be described by assuming that, as quite often occurs, the monitor M and the transducer T are on opposite sides of the patient's bed.
1. In order to prevent any alarms from being asserted during the zero calibration, a control A on the monitor M is activated so as to disable the alarm.
2. After walking around the bed, the nurse closes V.sub.2 and opens V.sub.3 so that atmospheric pressure is applied to the surface S of the transducer T.
3. In order to adjust the zero setting of the monitor, it is necessary to walk around the bed a second time so as to activate the zero setting control Z on the monitor M.
4. A third trip around the bed is required to close V.sub.2 and open V.sub.3 so that the blood pressure will be applied to the transducer T.
5. A fourth trip around the bed is required to activate the alarms with the control A.